The present invention relates generally to fluid pressure regulators, and more specifically, to pressure regulating valves convertible in the field with minimal parts replacement to separate output pressure ranges, such as those typically used in natural and LP fuel gas controls.
Applications have existed for some time for pressure regulating valves capable of regulating to either of two selected pressures. In general, these applications have been somewhat specialized, and the required volumes relatively small, thus providing little incentive for exploring nontraditional designs.
A pressure regulating valve requirement which impacts gas valve manufacturers and users results from the fact that both natural gas and gas produced from liquefied petroleum (LP) or propane are in common use as fuel gases. These gasses have different burning characteristics, and are supplied to a furnace or other burner apparatus under different pressures. Specifically, gas generated from liquefied petroleum has a faster flame front. Accordingly, it is supplied to a burner at a higher pressure, e.g., 10 inches H.sub.2 O, which induces more oxygen entrainment. In contrast, natural gas is typically supplied to a furnace or burner at a pressure of 3.5 inches H.sub.2 O. Accordingly, a pressure regulating gas valve for a furnace or other appliance must regulate to a higher pressure for LP gas than for natural gas.
There are various situations in which it is not known at the outset which type of fuel gas will be used, and/or in which the type of fuel gas may be changed at some point during the operating life of the furnace or other appliance. Either situation often occurs with a gas fireplace. Another common situation is in connection with new construction of a permanent fixed location dwellings. Initially natural gas may not be available because underground gas lines are not in place in the area, or because hook up to natural gas lines is delayed by frozen ground, or for other reasons.
Typical solutions in the past have been to either change out the entire gas valve at the time of conversion to a different fuel gas, or to replace certain components such as regulator springs or pressure regulator modules. Both of these solutions are undesirable for several reasons.
Although gas valves are available for operation with either natural gas or LP, an increasing need exists for a single gas valve with a simplified field selectable gas option.
The applicants have devised a design for such a valve which retains the advantageous features of prior limited purpose designs, while providing the capability of fuel type selection at the time of installation by replacement of a single simple part without disassembly of any other valve components.